Field of the Invention
This invention concerns a copper alloy excellent in migration resistance and, more specifically, it relates to a copper alloy excellent in migration resistance suitably used as material for electric and electronic components such as semiconductor parts, mechanical components, for examples, switching parts, bus bars, terminals and connectors, as well as printed circuit boards. As the material for the mechanical components such as terminals and connectors for use in home and industrial fields or in automobiles, brass has generally been used and phosphor bronze has been used in a case where reliability is particularly demanded.
However, brass involves the problem of stress corrosion crackings, while phosphor bronze may possibly cause migration under the conditions where condensation of moisture occurs.
Pure copper and Cu-Fe-P type alloys (CDA11000, CDA12200, CDA19200, CDA19210, and CDA19400) have often been used as the materials for electronic and electrical components for use in lead frames of semiconductor components and printed circuit boards.
Reduction in the size and the increase in the mounting density have rapidly been developed for the components constituted with the materials applied to the foregoing application uses due to the technical progress in recent years. In the electric or electronic components for use in home electric products such as coolers, television receivers and video tape recorders, as well as those mounted on automobiles, development has been made for the increase in the mounting density and the multi-layered structure of printed circuit boards, as well as reduction in the inter-electrode distance. In addition, improvement in the current capacity has also been attempted on one hand.
As a result, printed circuits or electrode portions are liable to suffer from the effects of condensated moistures or dusts (liable to absorb water) and electric fields, by which electrochemical migration occurs to reduce the insulation performance in conventional materials making it difficult to reduce the size and increase the mounting density.
Migration means herein such a phenomenon that metal elements are ionized upon condensation of moisture between electrodes, the ionized metal elements transfer to the cathode by means of a coulomb force and metal crystals are grown in a dendritic manner from the cathode and reach as far as the anode in the same manner as electroplating, to cause short circuitting between them.
Oxides are often formed to the inside and the surface of metal crystals depending on the circumstances such as drying or dewing, wherein substances between the electrodes are extended in the form of an extremely thin film along the surface of insulators such as plastic, glass and ceramic and often branched into plurality parts at the top end. This phenomenon occurs under the application of several to several tens of voltage and of several to several tens ampere of current. Although this has generally been considered to occur in silver, it has been found that such a phenomenon also possibly occur in copper and copper alloys with the recent development in the higher density mounting and increase in the number of constituent layers in printed circuit boards for electric or electronic components.
This migration problem occurs not only in the case of flooding due to moisture condensation but also occurs in the case where water is deposited to electric and electronic components caused by water leakage or the like and the advent of migration-resistant material has been demanded.